How historically accurate can you really get?

After reading the Book Thief, along with discussions in class about historical fiction, I've been thinking a lot about what it means for something to be historically accurate. As a means to decipher quality historical fiction books from bad ones we use this "historical accuracy" as a tool. I have had discussions in other classes about history and how history is relative. History in our textbooks change through out time depending on what perspective its written from. Classic example would be of Christopher Columbus. Growing up we learned that Columbus sailed the ocean blue and found America and was go great. Little was told about how he mutilated and killed many native Americans and how he thought he was in India, not the new world. Basically what I'm trying to get at is how are we suppose to judge something on its historical accuracy when besides the concrete facts of, this is what happened, all the rest is based on interpretations? and whats to say that one account is more valuable than another? Don't get me wrong, I do understand how some historical fiction books are better than others, but unless I'm reading a story that is based on the persons own accounts, how am I suppose to know how "accurate" it really is?